The present invention relates to a heat exchanger, particularly for use as a rack evaporator in refrigerators or freezers.
Refrigerators are known which are constituted by a box-like structure inside which a plurality of mutually stacked and spaced shelves is arranged to support the goods to be preserved.
In order to achieve higher efficiency of the refrigeration circuit and to keep the temperature inside the refrigerator or freezer as uniform as possible, in some types of refrigerator each shelf is constituted by a coil evaporator formed by means of a tubular body extending along a path that forms bends alternated with straight and substantially mutually co-planar portions. A structure is furthermore associated with the coil of each shelf and may be constituted by rods welded to the coils or by a plate-like element which is seamed or rigidly connected (for example by welding or glueing or other known rigid coupling methods) to the associated coil and has the purpose of forming a supporting surface for the products to be arranged on the shelves and, at the same time, of increasing the heat exchange surface of the coil.
In many kinds of these evaporators, indeed termed rack evaporators, the coils of the various shelves are formed by means of one or more tubular bodies which are variously folded so as to form the straight portions and the bends of each coil and mutually connect the coils of the various shelves.
During the manufacture of the entire evaporator and/or during surface treatment and/or handling, transport and packaging, it is sometimes necessary to apply an axial torsion to some appropriate straight portions of the tubular body, and in particular to one or both of the outermost portions of the set of parallel co-planar tube portions that forms, together with the bends, the coil of the individual shelf (this set is hereafter simply termed "grid").
This possibility exists, and is sometimes used, in the tubular system of evaporators in which the supporting and/or heat-exchange enhancement surface is constituted by a plate which is seamed to the grid (rotation by axial torsion of the tube inside the seams), whereas in the evaporator, in which the supporting and/or heat-exchange enhancement surface is constituted by metal rods welded to the grid that constitutes the individual shelf, this possibility has never been available, since the rods have always been welded or otherwise rigidly coupled to all of the above mentioned tube portions: the required angle of axial torsion is in fact usually such that it does not allow to discharge the entire torsion onto the small portion of tube that has no welds to the rods and is in any case such as to cause unacceptable deformations on the rods and/or deformations/breakages of the tube portion affected by the rotation.
In some types of rack evaporator there is an additional branch which is arranged proximate to one side of the shelf, is orientated at right angles to tile longer straight portions of the coil, and is not affected by the supporting structure constituted by the rods. Although this solution at least partially solves the problem of torsion on the additional branch, it has the drawback that it greatly complicates the production of the evaporator, indeed due to the arrangement of the additional branch, and for this reason it can be adopted with some benefit only in the manufacture of evaporators having at the most two shelves formed with a single curved tube, thus forcing to mutually connect multiple pairs of shelves by welding.